Don't farms cull their stock by 3 years old? What if living in total darkness means they grow large quickly but die by age 15?
Forgive my cynicism but my opinion is they're only there for profit, not for the best husbandry... I don't think they really care if the animal has diseases, as long as it grow out by that time..

Mr. F
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Real time Rogue, a captive Palp